This invention relates in general to composite structural elements formed of fiber reinforced thermoplastic material and to a method of manufacturing such elements.
The manufacture of structural elements from composite materials formed of high strength fibers embedded in a polymer matrix is well known in the art. Such composite materials have excellent strength to weight characteristics and, accordingly, have found wide application in situations where this characteristic is important. For the most part in the existing art, particular geometrical configurations are fabricated in the same process in which the composite material itself is produced. It is desirable, however, to produce composite structural members in a standardized form, such as elongated hollow tubes of various cross sections and wall thicknesses, and also elongated solid rods, again of varying cross sectional shapes cut to useful lengths or wound on drums as a continuous element. If such standardized structural elements can be produced which can thereafter be further processed to particular shapes for specific applications, such as tapered tubes or rods, or tubes or rods formed into helixes, then the standardized elements can be produced at one location and transported to a different location for processing into the geometric shapes suitable for any particular application and more flexible and economical manufacturing of complex articles can be achieved.
Processes for manufacture of such tubes and rods have been developed in the art. In general, the composite structure is formed of a series of layers or plies, where each ply may be the same or a different polymer and in which the fibers may be wrapped with different orientations or braiding patterns to suit the requirements of a particular structure. The processes employed and the apparatus for practicing these processes are well known to those skilled in the art. They include a pultrusion process, an extrusion process and for sheet like materials a roll forming process. Fiber materials which have been employed in the art include aramid fibers, glass fibers, carbon and graphite, as well as materials such as ceramics and boron. The polymer matrix material is normally a thermoset material such as polyester or epoxy resin. Additionally, a variety of thermoplastic materials such as nylon, polypropylene, polycarbonate and the like have been used.